1. Technical Field
The present invention relates to a circuit device and an electronic apparatus or the like.
2. Related Art
A technique of controlling the number of revolutions of a motor by controlling a chopping current is known as a technique for a motor driver that drives a DC motor. In this technique, a current flowing to an H-bridge circuit is converted to a voltage by a sense resistor, and the resultant voltage is compared with a reference voltage, to detect a chopping current. The detection result is fed back to a control circuit, to perform PWM control of a drive signal for the bridge circuit, thereby rotating a motor at a fixed rate. As such techniques for a motor driver, the techniques disclosed in JP-A-2003-189683 and JP-A-2008-042975 are known.
The H-bridge circuit of the motor driver has first to fourth transistors (switching elements) for driving, where the first and fourth transistors, and the second and third transistors, are connected electrically diagonally with respect to the motor. During the charge period, the first and fourth transistors are on, whereby the positive-side (+) terminal of the motor is set to a high-potential voltage and the negative-side (−) terminal is set to a low-potential voltage. During the decay period, the second and third transistors are on, whereby the positive-side terminal of the motor is set to a low-potential voltage and the negative-side terminal is set to a high-potential voltage.
When the period is switched from the charge period to the decay period as described above, an abrupt voltage change occurs at a node of a terminal of the motor. In this case, a gate capacitance (gate-drain capacitance) is present in a transistor for driving. It has been therefore found that, when an abrupt voltage change occurs at a node of a terminal of the motor, this voltage change is conveyed to the gate node of the transistor for driving via the gate capacitance, raising an abnormal condition such as that so-called self-turn-on occurs causing flow of a through current.